diff --git a/includes/resourceloader/DerivativeResourceLoaderContext.php b/includes/resourceloader/DerivativeResourceLoaderContext.php
index 5525a2222d5..aac3d452532 100644
--- a/includes/resourceloader/DerivativeResourceLoaderContext.php
+++ b/includes/resourceloader/DerivativeResourceLoaderContext.php
@@ -20,6 +20,8 @@
  */
 
 use MediaWiki\MediaWikiServices;
+use MediaWiki\User\UserFactory;
+use MediaWiki\User\UserIdentity;
 
 /**
  * A mutable version of ResourceLoaderContext.
@@ -48,6 +50,8 @@ class DerivativeResourceLoaderContext extends ResourceLoaderContext {
 	protected $skin = self::INHERIT_VALUE;
 	/** @var int|string|null */
 	protected $user = self::INHERIT_VALUE;
+	/** @var int|UserIdentity|null|false */
+	protected $userIdentity = self::INHERIT_VALUE;
 	/** @var int|User|null */
 	protected $userObj = self::INHERIT_VALUE;
 	/** @var int */
@@ -129,6 +133,25 @@ class DerivativeResourceLoaderContext extends ResourceLoaderContext {
 		return $this->user;
 	}
 
+	public function getUserIdentity(): ?UserIdentity {
+		if ( $this->userIdentity === self::INHERIT_VALUE ) {
+			return $this->context->getUserIdentity();
+		}
+		if ( $this->userIdentity === false ) {
+			$username = $this->getUser();
+			if ( $username === null ) {
+				// Anonymous user
+				$this->userIdentity = null;
+			} else {
+				// Use provided username if valid
+				$this->userIdentity = MediaWikiServices::getInstance()
+					->getUserFactory()
+					->newFromName( $username, UserFactory::RIGOR_VALID );
+			}
+		}
+		return $this->userIdentity;
+	}
+
 	public function getUserObj(): User {
 		if ( $this->userObj === self::INHERIT_VALUE ) {
 			return $this->context->getUserObj();
@@ -152,6 +175,7 @@ class DerivativeResourceLoaderContext extends ResourceLoaderContext {
 		$this->hash = null;
 		// Clear getUserObj cache
 		$this->userObj = null;
+		$this->userIdentity = false;
 	}
 
 	public function getDebug(): int {
diff --git a/includes/resourceloader/ResourceLoaderContext.php b/includes/resourceloader/ResourceLoaderContext.php
index 4144c5b6431..89d6e0683d5 100644
--- a/includes/resourceloader/ResourceLoaderContext.php
+++ b/includes/resourceloader/ResourceLoaderContext.php
@@ -23,6 +23,8 @@
 use MediaWiki\Logger\LoggerFactory;
 use MediaWiki\MediaWikiServices;
 use MediaWiki\Page\PageReferenceValue;
+use MediaWiki\User\UserFactory;
+use MediaWiki\User\UserIdentity;
 use Psr\Log\LoggerInterface;
 
 /**
@@ -81,6 +83,8 @@ class ResourceLoaderContext implements MessageLocalizer {
 	protected $hash;
 	/** @var User|null */
 	protected $userObj;
+	/** @var UserIdentity|null|false */
+	protected $userIdentity = false;
 	/** @var ResourceLoaderImage|false */
 	protected $imageObj;
 
@@ -261,6 +265,31 @@ class ResourceLoaderContext implements MessageLocalizer {
 			->page( PageReferenceValue::localReference( NS_SPECIAL, 'Badtitle/ResourceLoaderContext' ) );
 	}
 
+	/**
+	 * Get the possibly-cached UserIdentity object for the specified username
+	 *
+	 * This will be null on most requests,
+	 * except for load.php requests that have a 'user' parameter set.
+	 *
+	 * @since 1.38
+	 * @return UserIdentity|null
+	 */
+	public function getUserIdentity(): ?UserIdentity {
+		if ( $this->userIdentity === false ) {
+			$username = $this->getUser();
+			if ( $username === null ) {
+				// Anonymous user
+				$this->userIdentity = null;
+			} else {
+				// Use provided username if valid
+				$this->userIdentity = MediaWikiServices::getInstance()
+					->getUserFactory()
+					->newFromName( $username, UserFactory::RIGOR_VALID );
+			}
+		}
+		return $this->userIdentity;
+	}
+
 	/**
 	 * Get the possibly-cached User object for the specified username
 	 *
diff --git a/includes/resourceloader/ResourceLoaderUserModule.php b/includes/resourceloader/ResourceLoaderUserModule.php
index a51187909d1..393485dbff3 100644
--- a/includes/resourceloader/ResourceLoaderUserModule.php
+++ b/includes/resourceloader/ResourceLoaderUserModule.php
@@ -37,17 +37,18 @@ class ResourceLoaderUserModule extends ResourceLoaderWikiModule {
 	 * @return array[]
 	 */
 	protected function getPages( ResourceLoaderContext $context ) {
-		$config = $this->getConfig();
-		$user = $context->getUserObj();
-		if ( !$user->isRegistered() ) {
+		$user = $context->getUserIdentity();
+		if ( !$user || !$user->isRegistered() ) {
 			return [];
 		}
 
-		// Use localised/normalised variant to ensure $excludepage matches
-		$userPage = $user->getUserPage()->getPrefixedDBkey();
+		$config = $this->getConfig();
 		$pages = [];
 
 		if ( $config->get( 'AllowUserJs' ) ) {
+			$titleFormatter = MediaWikiServices::getInstance()->getTitleFormatter();
+			// Use localised/normalised variant to ensure $excludepage matches
+			$userPage = $titleFormatter->getPrefixedDBkey( new TitleValue( NS_USER, $user->getName() ) );
 			$pages["$userPage/common.js"] = [ 'type' => 'script' ];
 			$pages["$userPage/" . $context->getSkin() . '.js'] = [ 'type' => 'script' ];
 		}
diff --git a/includes/resourceloader/ResourceLoaderUserOptionsModule.php b/includes/resourceloader/ResourceLoaderUserOptionsModule.php
index 06496702324..65dff822b27 100644
--- a/includes/resourceloader/ResourceLoaderUserOptionsModule.php
+++ b/includes/resourceloader/ResourceLoaderUserOptionsModule.php
@@ -53,6 +53,7 @@ class ResourceLoaderUserOptionsModule extends ResourceLoaderModule {
 		$user = $context->getUserObj();
 
 		$tokens = [
+			// Replacement is tricky - T287542
 			'patrolToken' => $user->getEditToken( 'patrol' ),
 			'watchToken' => $user->getEditToken( 'watch' ),
 			'csrfToken' => $user->getEditToken(),
diff --git a/includes/resourceloader/ResourceLoaderUserStylesModule.php b/includes/resourceloader/ResourceLoaderUserStylesModule.php
index 3abcd497202..3e4680e6f73 100644
--- a/includes/resourceloader/ResourceLoaderUserStylesModule.php
+++ b/includes/resourceloader/ResourceLoaderUserStylesModule.php
@@ -38,17 +38,18 @@ class ResourceLoaderUserStylesModule extends ResourceLoaderWikiModule {
 	 * @return array[]
 	 */
 	protected function getPages( ResourceLoaderContext $context ) {
-		$config = $this->getConfig();
-		$user = $context->getUserObj();
-		if ( !$user->isRegistered() ) {
+		$user = $context->getUserIdentity();
+		if ( !$user || !$user->isRegistered() ) {
 			return [];
 		}
 
-		// Use localised/normalised variant to ensure $excludepage matches
-		$userPage = $user->getUserPage()->getPrefixedDBkey();
+		$config = $this->getConfig();
 		$pages = [];
 
 		if ( $config->get( 'AllowUserCss' ) ) {
+			$titleFormatter = MediaWikiServices::getInstance()->getTitleFormatter();
+			// Use localised/normalised variant to ensure $excludepage matches
+			$userPage = $titleFormatter->getPrefixedDBkey( new TitleValue( NS_USER, $user->getName() ) );
 			$pages["$userPage/common.css"] = [ 'type' => 'style' ];
 			$pages["$userPage/" . $context->getSkin() . '.css'] = [ 'type' => 'style' ];
 		}
diff --git a/tests/phpunit/includes/resourceloader/DerivativeResourceLoaderContextTest.php b/tests/phpunit/includes/resourceloader/DerivativeResourceLoaderContextTest.php
index 0c33e054cde..d99ae4700a7 100644
--- a/tests/phpunit/includes/resourceloader/DerivativeResourceLoaderContextTest.php
+++ b/tests/phpunit/includes/resourceloader/DerivativeResourceLoaderContextTest.php
@@ -1,5 +1,7 @@
 <?php
 
+use MediaWiki\User\UserIdentity;
+
 /**
  * @group ResourceLoader
  * @covers DerivativeResourceLoaderContext
@@ -66,17 +68,24 @@ class DerivativeResourceLoaderContextTest extends MediaWikiIntegrationTestCase {
 
 	public function testChangeUserObj() {
 		$user = $this->createMock( User::class );
+		$userIdentity = $this->createMock( UserIdentity::class );
 		$parent = $this->createMock( ResourceLoaderContext::class );
 		$parent
 			->expects( $this->once() )
 			->method( 'getUserObj' )
 			->willReturn( $user );
+		$parent
+			->expects( $this->once() )
+			->method( 'getUserIdentity' )
+			->willReturn( $userIdentity );
 
 		$derived = new DerivativeResourceLoaderContext( $parent );
 		$this->assertSame( $derived->getUserObj(), $user, 'inherit from parent' );
+		$this->assertSame( $derived->getUserIdentity(), $userIdentity, 'inherit from parent' );
 
 		$derived->setUser( null );
 		$this->assertNotSame( $derived->getUserObj(), $user, 'different' );
+		$this->assertNull( $derived->getUserIdentity(), 'no user identity' );
 	}
 
 	public function testChangeDebug() {
diff --git a/tests/phpunit/includes/resourceloader/ResourceLoaderContextTest.php b/tests/phpunit/includes/resourceloader/ResourceLoaderContextTest.php
index dac55ae4459..c3ccce9b453 100644
--- a/tests/phpunit/includes/resourceloader/ResourceLoaderContextTest.php
+++ b/tests/phpunit/includes/resourceloader/ResourceLoaderContextTest.php
@@ -35,6 +35,7 @@ class ResourceLoaderContextTest extends PHPUnit\Framework\TestCase {
 		$this->assertEquals( 'qqx|fallback|0|||||||', $ctx->getHash() );
 		$this->assertSame( [], $ctx->getReqBase() );
 		$this->assertInstanceOf( User::class, $ctx->getUserObj() );
+		$this->assertNull( $ctx->getUserIdentity() );
 	}
 
 	public function testDummy() {
@@ -134,12 +135,14 @@ class ResourceLoaderContextTest extends PHPUnit\Framework\TestCase {
 		$ctx = new ResourceLoaderContext( $this->getResourceLoader(), new FauxRequest( [] ) );
 		$this->assertSame( null, $ctx->getUser() );
 		$this->assertFalse( $ctx->getUserObj()->isRegistered() );
+		$this->assertNull( $ctx->getUserIdentity() );
 
 		$ctx = new ResourceLoaderContext( $this->getResourceLoader(), new FauxRequest( [
 			'user' => 'Example'
 		] ) );
 		$this->assertSame( 'Example', $ctx->getUser() );
 		$this->assertEquals( 'Example', $ctx->getUserObj()->getName() );
+		$this->assertEquals( 'Example', $ctx->getUserIdentity()->getName() );
 	}
 
 	public function testMsg() {